Gas diffusion electrode equipped ion exchange membrane electrolyzer

ABSTRACT

Provided is a gas diffusion electrode equipped ion exchange membrane electrolyzer including an anode, an ion-exchange membrane, and a cathode chamber in which a gas diffusion electrode is disposed, wherein in a cathode gas chamber formed between a back plate of the cathode chamber and one side of the gas diffusion electrode opposite to the electrolytic surface, a gas-permeable elastic member is disposed between the gas diffusion electrode and the back plate, and the elastic member forms a conductive connection between the gas diffusion electrode and the back plate by making contact with corrosion-resistant conductive layers formed on the surfaces of a plurality of conductive members which are joined to the back plate.

TECHNICAL FIELD

The present invention relates to a gas diffusion electrode equipped ionexchange membrane electrolyzer for use in electrolysis of an alkalimetal chloride aqueous solution such as brine and, more particularly, toa gas diffusion electrode equipped ion exchange membrane electrolyzersuitably applied to a two-chamber type gas diffusion electrode equippedion exchange membrane electrolyzer.

BACKGROUND ART

A gas diffusion electrode equipped ion exchange membrane electrolyzerprovided with a gas diffusion electrode is utilized as a means forreducing electrolysis voltage by causing a reaction with a gasintroduced from outside at the gas diffusion electrode.

In a gas diffusion electrode equipped ion exchange membrane electrolyzerfor alkali metal chloride aqueous solution wherein the gas diffusionelectrode is used as a cathode, an alkali chloride aqueous solution issupplied to an anode chamber so as to generate a chlorine gas at ananode. On the other hand, an oxygen-containing gas is supplied to acathode chamber, whereby at the gas diffusion electrode, the oxygen isreduced, and further, an alkali metal hydroxide aqueous solution isgenerated.

An electrolyte cannot be made to flow over the entire surface of the gasdiffusion electrode unless a state where the gas diffusion electrode isbrought into firm and uniform contact to the ion exchange membrane ismaintained. If not, a current cannot be made to flow uniformly throughthe electrolytic surface of the gas diffusion electrode.

To cope with this, there has been proposed an ion exchange membraneelectrolyzer in which a gas-permeable elastic member is disposed betweena cathode chamber at the back of the gas diffusion electrode and a backplate so as to bring the gas diffusion electrode into firm contact withthe ion exchange membrane and to ensure electrical conduction betweenthe back plate of the cathode chamber and gas diffusion electrode.

Since the alkali metal hydroxide aqueous solution and oxygen exist inthe cathode chamber, an oxidizing environment is formed along the innerwall surface of the cathode chamber. Therefore, the cathode chamber ismade of nickel, a nickel alloy, or the like. However, under such anenvironment, a passivation film is formed on the surface of the nickelor nickel alloy due to oxidation.

Although progression of metal corrosion can be restrained by thepassivation film formed on the nickel or nickel alloy, a largeconduction resistance is generated by the passivation film in aconducting circuit through which a current is made to flow by thecontact of the elastic member with the back plate of the cathode chamberand the gas diffusion electrode.

To prevent a reduction in the conductivity due to the passivation film,there has been proposed a configuration in which silver plating isapplied to the back plate of the cathode chamber and elastic member soas to prevent an increase in the conduction resistance (refer to e.g.,Patent Document 1).

Citation List Patent Document

Patent Document 1: JP-A-2006-322018

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Although to prevent a reduction in the conductivity and prevent anincrease in the conduction resistance by applying silver plating to theback plate of the cathode chamber and elastic member is an effectivemeans for preventing an increase in the voltage of the gas diffusionelectrode equipped ion exchange membrane electrolyzer, it has not beenpossible to avoid the increase in the voltage of the electrolyzer undera long duration of electrolysis.

An object of the present invention is to provide a gas diffusionelectrode equipped ion exchange membrane electrolyzer capable ofpreventing an increase in the voltage of the electrolyzer due to anincrease in the conduction resistance in the conducting circuit from thegas diffusion electrode to the back plate of the cathode chamber so asto perform a lower voltage operation which is one of the features of thegas diffusion electrode equipped ion exchange membrane electrolyzer fora long period of time.

Means for Solving the Problems

According to the present invention, there is provided a gas diffusionelectrode equipped ion exchange membrane electrolyzer having an anode,an ion exchange membrane, and a cathode chamber in which a gas diffusionelectrode is disposed, characterized in that in a cathode gas chamberformed between a back plate of the cathode chamber and one side of thegas diffusion electrode opposite to the electrolytic surface, agas-permeable elastic member is disposed between the gas diffusionelectrode and the back plate, and the elastic member forms a conductiveconnection between the gas diffusion electrode and the back plate bymaking contact with corrosion-resistant conductive layers formed on thesurfaces of a plurality of conductive members which are joined to theback plate.

The conductive member has a silver or platinum group metal-containingcorrosion-resistant conductive layer on a foil or plate made of nickelor a nickel alloy.

The conductive member is obtained by integrating the silver or platinumgroup metal-containing corrosion-resistant conductive layer by means ofplating, cladding or baking coating.

A part of or the entire conductive member is joined to the back plate.

The elastic member forms a corrosion-resistant conductive layer on aconductive contacting surface or the entire surface thereof.

Advantages of the Invention

The gas diffusion electrode equipped ion exchange membrane electrolyzeraccording to the present invention has a configuration in which theplurality of conductive members on the surface of each of which thecorrosion-resistant conductive layer is formed are disposed on thesurfaces contacting the elastic member and back plate of the cathodechamber for electrical conduction to the gas diffusion electrode. As aresult, there can be provided a gas diffusion electrode equipped ionexchange membrane electrolyzer in which characteristics of the contactportion with the elastic member for electrical conduction to the gasdiffusion electrode are stable, and the voltage of the electrolyzer canstably be kept at a lower level for a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view for explaining an embodiment of a gasdiffusion electrode equipped ion exchange membrane electrolyzeraccording to the present invention.

FIG. 2 is an exploded perspective view for explaining the embodiment ofthe gas diffusion electrode equipped ion exchange membrane electrolyzeraccording to the present invention.

FIGS. 3A and 3B are views for explaining the embodiment of the gasdiffusion electrode equipped ion exchange membrane electrolyzeraccording to the present invention, which illustrate the conductivemember, and in which FIG. 3A illustrates an example in which conductivemembers each having a comparatively large area are mounted to the backplate, and FIG. 3B illustrates an example in which a large number ofconductive members each having a comparatively small area are mounted tothe back plate.

FIG. 4 is a view for explaining Example and Comparative Example of thegas diffusion electrode equipped ion exchange membrane electrolyzeraccording to the present invention.

FIG. 5 is a view for explaining the embodiment of the gas diffusionelectrode equipped ion exchange membrane electrolyzer according to thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

It has been found that partial separation of a coating layer of amaterial excellent in conductivity such as silver formed on theconduction contacting surface of a back plate of a cathode chamber of agas diffusion electrode equipped ion exchange membrane electrolyzer iscaused by an occurrence of portions different in electrochemicalcharacteristics due to unevenness in the film thickness occurring in thecoating layer formed by plating or the like.

That is, the back plate of the cathode chamber is surrounded by acathode chamber frame, so that it is not possible to avoid an occurrenceof a phenomenon in which unevenness occurs in the flow of a platingsolution in a plating tank, causing formation of portions different incharacteristics such as film thickness. Thus, when electrolysis isperformed for a long period of time, a problem such as film separationfrom the back plate may occur.

In the present invention, a problem caused by directly plating aconductive layer to the back plate is solved as follows. That is, aplurality of conductive members made of a planar metal foil or metalplate formed by plating a corrosion-resistant conductive layer made ofsilver or platinum-group metal to the surface thereof are joined to theback plate so as to make the characteristics of the contacting portionto an elastic member uniform, thereby allowing prevention of aphenomenon such as separation of the corrosion-resistant conductivelayer contacting the elastic member.

An embodiment of the present invention will be described with referenceto the accompanying drawings.

FIG. 1 is a cross-sectional view for explaining an embodiment of a gasdiffusion electrode equipped ion exchange membrane electrolyzeraccording to the present invention.

The following description is made taking a gas diffusion electrodeequipped ion exchange membrane electrolyzer for use in electrolysis ofbrine, in which a single anode chamber and a single cathode chamber arestacked through an ion exchange membrane.

FIG. 1 is a cross-sectional view obtained by cutting the gas diffusionelectrode equipped ion exchange membrane electrolyzer along a planeorthogonal to an electrode surface.

A gas diffusion electrode equipped ion exchange membrane electrolyzer 1has a configuration called a two-chamber type gas diffusion electrodeequipped ion exchange membrane electrolyzer, in which an anode chamber20 and a cathode chamber 30 provided therein are separated by an ionexchange membrane 10.

The anode chamber 20 has an anode 211 and is filled with brine as ananolyte 213. An anolyte inlet 215 is formed at the lower portion of theanode chamber 20.

An outlet 217 for anolyte whose concentration has been decreased byelectrolysis and gas is formed at the upper portion of the anodechamber, and an anode chamber frame 219 is stacked to the ion exchangemembrane 10 through an anode chamber side gasket 221.

The cathode chamber 30 is provided on the opposite side to the anodechamber 20 with respect to the ion exchange membrane 10, and a gasdiffusion electrode 313 is provided in the cathode chamber.

A liquid retaining member 311 is disposed between a cathode chamberinner space 301 including the gas diffusion electrode 313 and ionexchange membrane 10.

On one side of the gas diffusion electrode 313 opposite to the liquidretaining member 311 side, an elastic member 330 which is made of a wirerod and which has inside thereof a space through which a gas can bepassed is disposed.

The elastic member 330 brings the gas diffusion electrode 313 and liquidretaining member 311 into firm contact with the ion exchange membrane 10side to forma cathode gas chamber 317 within the cathode chamber andmakes contact with corrosion-resistant conductive layers 341 formed onthe surfaces of a plurality of conductive members 340 which are joinedto the back plate 327 of the cathode chamber 30 to form a conductingcircuit between the gas diffusion electrode 313 and back plate 327.

When an alkali metal chloride aqueous solution is supplied to the anodechamber 20 of the gas diffusion electrode equipped ion exchange membraneelectrolyzer 1 according to the present invention and then current isapplied between the anode 211 and gas diffusion electrode 313 while anoxygen-containing gas is supplied to the cathode gas chamber 317 of thecathode chamber 30 through an oxygen inlet 319, the gas diffusionelectrode 313 is supplied with the fluid content of an alkali metalhydroxide aqueous solution from the liquid retaining member 311 as wellas supplied with the oxygen-containing gas from the cathode gas chamber317 side, resulting in progress of a generating reaction of the alkalimetal hydroxide aqueous solution in the gas diffusion electrode 313.

The generated alkali metal hydroxide aqueous solution is transferred tothe liquid retaining member 311 according to the concentration gradientand absorbed/retained by the liquid retaining member 311, as well asflows down along the inside of the liquid retaining member 311 and gaschamber side of the gas diffusion electrode 313 to be discharged from acathode gas chamber outlet 321.

Since a high concentration oxygen, a water vapor, and mist of the alkalimetal hydroxide aqueous solution exist in the cathode gas chamber 317,and temperature of the cathode gas chamber 317 reaches about 90° C., thecathode chamber is made of nickel, a nickel alloy, or the like. Further,the elastic member is made of a metal material having a high corrosionresistance and a high conductivity, such as nickel or a high nickelalloy.

In a conventional gas diffusion electrode equipped ion exchange membraneelectrolyzer, a metal having a satisfactory corrosion resistance, suchas nickel or a nickel alloy, used as a material of the cathode gaschamber 317 is oxidized at its surface in the presence of a highconcentration oxygen to form a passivation film, impeding electricalconduction, which leads to an increase in the voltage of theelectrolyzer.

To cope with this, in the gas diffusion electrode equipped ion exchangemembrane electrolyzer according to the present invention, a plurality ofplanar conductive members 340 each having a corrosion-resistantconductive layer 341 on the surface thereof are disposed on the backplate 327 of the cathode chamber 30.

Each planar conductive member 340 has the corrosion-resistant conductivelayer 341 whose surface characteristics are made uniform by plating,cladding, or baking coating, so that even if the area of the back plate327 is increased, a surface having uniform characteristics can beobtained in any position.

As a result, in a long period operation, an increase in a contactresistance does not occur at the contacting surfaces of the elasticmember 330 forming the conducting circuit between the gas diffusionelectrode 313 and back plate 327 due to existence of thecorrosion-resistant conductive layers 341, allowing prevention of anincrease in the voltage of the electrolyzer.

As the planar conductive member, it is preferable to use the samematerial as that of the back plate of the cathode chamber, i.e., anickel material, the thickness thereof preferably being 0.1 mm to 1.0mm. The corrosion-resistant conductive layer maybe formed of a metalsuch as silver or platinum group metal and it is particularly preferableto use silver having a satisfactory conductivity. Thecorrosion-resistant conductive layer can be formed by plating, cladding,baking, or the like.

The thickness of the corrosion-resistant conductive layer is preferablyset to 0.5 μm or more. When the thickness falls below 0.5 μm, sufficientcharacteristics cannot be obtained. On the other hand, the larger thethickness, the more excellent the corrosion resistance and the likebecome; however, a thickness of about 5 μm will suffice.

It is preferable that the planar conductive member is formed in a sizeof 60 mm×56 mm to 1220 mm×500 mm. When the size is smaller than 60 mm×56mm, the number of the planar conductive members to be installed isincreased to increase the number of spot welding points, which mayresult in a degradation of the uniformity. On the other hand, when thesize is larger than 1220 mm×500 mm, nonuniformity is likely to occurunfavorably when the corrosion-resistant conductive layer is formed byplating or the like.

FIG. 2 is a view for explaining the embodiment of the gas diffusionelectrode equipped ion exchange membrane electrolyzer according to thepresent invention and more specifically, an exploded perspective viewfor explaining the elastic member and conductive member.

The plurality of conductive members 340 are joined to the back plate 327of a cathode chamber frame 323. In the illustrative example, 12conductive members 340 are disposed.

The elastic member 330 is disposed such that one surface thereofcontacts the conductive members 340 and the other surface thereofcontacts one surface of the gas diffusion electrode opposite to theelectrolytic surface.

In the example of FIG. 2, the elastic member 330 has eight unit elasticmembers 333 a, 333 b, 333 c, 333 d, 333 e, 333 f, 333 g, and 333 hmounted to an elastic member frame 331, each of which is constituted bya hollow spring coil forming a gas passage and is disposed so as touniformly press the gas diffusion electrode and to allow uniformelectrical conduction between the gas diffusion electrode and backplate.

The use of the plurality of unit elastic members can allow the pressureand current distribution uniformly applied to the gas diffusionelectrode even when the electrolysis area of the gas diffusion electrodeis increased. Further, the number of the unit elastic members 333 a to333 h forming the elastic member 330 and the number of the conductivemembers may appropriately be set in accordance with the size of theelectrolysis area or magnitude of the application current density.

FIG. 3 is a view for explaining the embodiment of the gas diffusionelectrode equipped ion exchange membrane electrolyzer according to thepresent invention, which illustrates the conductive member.

In the example of FIG. 3A, conductive members 340 each having acomparatively large area are mounted to the back plate by a method suchas spot welding performed at joining portions 343 and thecorrosion-resistant conductive layers 341 formed on the conductivemembers 340 are disposed on the gas diffusion electrode side.

In the example of FIG. 3B, a large number of conductive members 340 eachhaving a smaller area than the conductive members of FIG. 3A are mountedto the back plate 327 and joined thereto at the joining portions 343,and corrosion-resistant conductive layers 341 are formed respectively onthe surface of the mounted conductive members.

The mounting of a large number of the small-area conductive members 340allows stable electrical conduction between the back plate and gasdiffusion electrode for a long period of time.

Hereinafter, the present invention will be described based on Examplesand Comparative Examples.

EXAMPLE Example 1

An ion exchange membrane (anode ion exchange membrane F-8020 made byAsahi Glass Co., Ltd) was disposed in an electrolyzer having aneffective electrolysis area of 56 mm (height)×60 mm (width) so as tocontact an anode for brine electrolysis (JP202R made by PermelecElectrode Ltd.). On the opposite side of the anode of the ion exchangemembrane, a carbon fiber fabric (made by Zoltek) having a thickness of0.4 mm that covers the electrolytic surface was stacked as a liquidretaining member, and further a liquid-permeable gas diffusion electrode(Permelec Electrode Ltd.) was stacked on the liquid retaining member.

A nickel wire coil obtained by winding a nickel wire having a wirediameter of 0.17 mm in a coil shape having a winding diameter of 6 mmwas disposed on one side of the gas diffusion electrode opposite to theelectrolytic surface.

A conductive member made of a nickel foil (NW2201) of 56 mm (H)×60 mm(W)×0.2 mm (T) having one surface that has been subjected to silverplating was joined to the back plate of the cathode chamber of thecathode chamber frame by spot welding at six points.

A voltage measurement terminal was attached to the gas diffusionelectrode, and the electrolyzer was operated for 17 days with thecurrent density kept at 3 kA/m², electrolysis temperature kept at 87° C.to 89° C., and aqueous sodium hydroxide concentration kept at 30 mass %to 33 mass %.

A potential difference between the gas diffusion electrode and backplate, i.e., voltage drop was measured. The measurement result is shownin FIG. 4. A voltage was not increased but kept at an initial voltage of0.001 V, that is, operation of the electrolyzer was stable for 17 days.

Example 2

An ion exchange membrane (anode ion exchange membrane “Aciplex” F-4403made by Asahi Kasei Chemicals Corporation) was disposed in anelectrolyzer having an effective electrolysis area of 620 mm(width)×1220 mm (height) so as to contact an anode for brineelectrolysis (JP202R made by Permelec Electrode Ltd.). On the oppositeside of the anode of the ion exchange membrane, a carbon fiber fabric(made by Zoltek) having a thickness of 0.4 mm that covers theelectrolytic surface was stacked as a liquid retaining member, andfurther a liquid-permeable gas diffusion electrode (Permelec ElectrodeLtd.) was stacked on the liquid retaining member.

Four nickel wire coils each obtained by winding a nickel wire having awire diameter of 0.17 mm in a coil shape having a winding diameter of 6mm were disposed on one surface of the gas diffusion electrode oppositeto the electrolytic surface.

Two conductive members each made of a nickel foil (NW2201) of 1160 mm(H)×310 mm (W)×0.2 mm (T) having one surface that has been subjected tosilver plating of a 10 μm thickness were each joined to the back plateof the cathode chamber of the cathode chamber frame by spot welding at144 points.

Thus obtained electrolyzer was used to perform electrolysis with thecurrent density kept at 3 kA/m², electrolysis temperature kept at 75° C.to 85° C., and aqueous sodium hydroxide concentration kept at 30 mass %to 34 mass %.

As illustrated in FIG. 5 showing a trend in the voltage of theelectrolyzer, an increase in the voltage was not observed.

When the electrolyzer was disassembled after the total operation periodof 500 days, no abnormality was observed in the silver plated conductivemember.

Comparative Example 1

An electrolyzer produced in the same manner as Example 1 except that thesilver plating was not applied to the conductive member was used toperform electrolysis under the same conditions as those in Example 1,and a potential difference between the gas diffusion electrode and backplate of the cathode chamber was measured in the same manner asExample 1. As illustrated in FIG. 4 showing the measurement result, thepotential difference was increased with time.

Further, when the electrolyzer was disassembled after stop of theoperation, the nickel foil used as the conducting member was turnedblack due to formation of a passivation film.

Comparative Example 2

Electrolysis was performed in the same manner as Example 2 except thatan electrolyzer has a cathode chamber in which the conductive member wasnot provided and silver plating of a 10 μm center thickness was appliedto the back plate, and a trend in the voltage of the electrolyzer wasmeasured.

A 200 mV voltage increase was observed after 300 days operation.Further, when the electrolyzer was disassembled after stop of theoperation, the silver plating at substantially all the conductingportions of the silver plating layer of the back plate contacting theelastic member were separated to expose the nickel material as theunderlayer, and further, the nickel material as the underlayer wasturned black due to formation of a passivation film.

INDUSTRIAL APPLICABILITY

The gas diffusion electrode equipped ion exchange membrane electrolyzeraccording to the present invention has a configuration in which theplurality of conductive members on the surface of each of which thecorrosion-resistant conductive layer is formed are disposed on thesurfaces contacting the elastic member and back plate of the cathodechamber for electrical conduction to the gas diffusion electrode. As aresult, there can be provided a gas diffusion electrode equipped ionexchange membrane electrolyzer in which characteristics of the contactportion with the elastic member for electrical conduction to the gasdiffusion electrode are stable, no separation of the corrosion-resistantconductive layer from the surface of the conductive member occurs,voltage drop between the gas diffusion electrode and back plate issmall, and performance can be made stable for a long period of time.

EXPLANATION OF SYMBOLS

1: Gas diffusion electrode equipped ion exchange membrane electrolyzer

10: Ion exchange membrane

20: Anode chamber

30: Cathode chamber

211: Anode

213: Anolyte

215: Anolyte inlet

217: Anolyte and gas outlet

219: Anode chamber frame

221: Anode chamber side gasket

301: Cathode chamber inner space

311: Liquid retaining member

313: Gas diffusion electrode

317: Cathode gas chamber

319: Oxygen inlet

321: Cathode gas chamber outlet

323: Cathode chamber frame

325: Cathode chamber side gasket

327: Back plate

330: Elastic member

331: Elastic member frame

333 a, 333 b, 333 c, 333 d, 333 e, 333 f, 333 g, 333 h: Unit elasticmember

340: Conductive member

341: Corrosion-resistant conductive layer

343: Joining portion

1. A gas diffusion electrode equipped ion exchange membrane electrolyzerhaving an anode, an ion exchange membrane, and a cathode chamber inwhich a gas diffusion electrode is disposed, characterized in that in acathode gas chamber formed between a back plate of the cathode chamberand one side of the gas diffusion electrode opposite to the electrolyticsurface, a gas-permeable elastic member is disposed between the gasdiffusion electrode and the back plate, and the elastic member forms aconductive connection between the gas diffusion electrode and the backplate by making contact with corrosion-resistant conductive layersformed on the surfaces of a plurality of conductive members which arejoined to the back plate.
 2. The gas diffusion electrode equipped ionexchange membrane electrolyzer according to claim 1, characterized inthat the conductive member has a silver or platinum groupmetal-containing corrosion-resistant conductive layer on a foil or platemade of nickel or a nickel alloy.
 3. The gas diffusion electrodeequipped ion exchange membrane electrolyzer according to claim 1,characterized in that the conductive member is obtained by integratingthe silver or platinum group metal-containing corrosion-resistantconductive layer by means of plating, cladding or baking coating.
 4. Thegas diffusion electrode equipped ion exchange membrane electrolyzeraccording to claim 1, characterized in that a part of or the entireconductive member is joined to the back plate.
 5. The gas diffusionelectrode equipped ion exchange membrane electrolyzer according to claim1, characterized in that the elastic member forms a corrosion-resistantconductive layer on a conductive contacting surface or the entiresurface thereof.
 6. A manufacturing method of an alkali metal hydroxideaqueous solution, comprising: providing a gas diffusion electrodeequipped ion exchange membrane electrolyzer having an anode, an ionexchange membrane, and a cathode chamber in which a gas diffusionelectrode is disposed, characterized in that, in a cathode gas chamberformed between a back plate of the cathode chamber and one side of thegas diffusion electrode opposite to the electrolytic surface, agas-permeable elastic member is disposed between the gas diffusionelectrode and the back plate, and the elastic member forms a conductiveconnection between the gas diffusion electrode and the back plate bymaking contact with corrosion-resistant conductive layers formed on thesurfaces of a plurality of conductive members which are joined to theback plate; and using the gas diffusion electrode to manufacture analkali metal hydroxide aqueous solution.
 7. a manufacturing method ofchlorine, comprising: providing a gas diffusion electrode equipped ionexchange membrane electrolyzer having an anode, an ion exchangemembrane, and a cathode chamber in which a gas diffusion electrode isdisposed, characterized in that, in a cathode gas chamber formed betweena back plate of the cathode chamber and one side of the gas diffusionelectrode opposite to the electrolytic surface, a gas-permeable elasticmember is disposed between the gas diffusion electrode and the backplate, and the elastic member forms a conductive connection between thegas diffusion electrode and the back plate by making contact withcorrosion-resistant conductive layers formed on the surfaces of aplurality of conductive members which are joined to the back plate; andusing the gas diffusion electrode to manufacture chlorine.